Russia and Ukraine

[Angrboda]

I think the assessments of what it would take to pacify Ukraine are overblown.  March in, take the TV and radio stations, install a puppet regime, wait two weeks for the protests to die down while Europe and America rattle their sabers, and then leave, perhaps leaving token security forces behind.

of 100,000 troops on Ukrainian border, at most half that would actually be combat units.   Marching  all the way to Kiev with 2-3 divisions worth and then not getting cut off and surrounded is not trivial because the Ukrainian army is twice as large and has a disproportionate amount of leftover Soviet hardware to draw upon. 

The only way for that to succeed is if the effort is supported by an extensive fifth column in Ukraine and much of the Ukrainian army more or less melt away after the first shot.

It's mostly urban warfare. A divided populace goes a long way.